1. Technical Field
This invention relates generally to electronic control systems, and more particularly to an electronic control system adapted to help control the various functions of a powershift transmission of a heavy-duty, off-road vehicle such as an earth moving vehicle, and to provide pulse-width modulated control of the clutch of the transmission of the vehicle.
2. Discussion
Electronic control systems have been used to help control various functions of powershift transmission systems of off-road vehicles such as heavy-duty earth moving equipment. More specifically, such systems are adapted to read and respond to various solenoids and switches which have outputs indicative of a wide variety of operating parameters such as vehicle speed, vehicle load, etc. Most particularly, such electronic control systems are helpful for providing smoother clutch engagement of a transmission in large off-road vehicles such as earth moving vehicles, where the need for smooth clutch engagement becomes particularly acute. Abrupt engagement of the clutch of such a large and heavy vehicle can contribute significantly to premature clutch wear and even damage to drive-line components of the vehicle.
Many of the problems in controlling transmissions of heavy duty off-road vehicles are discussed in U.S. Pat. No. 4,855,913, entitled "Electronic Control System For Powershift Transmission", to Brekkestran, et al., issued Aug. 8, 1989, the disclosure of which is hereby incorporated by reference. The electronic control system disclosed in this patent represents a significant step forward in overcoming several problems associated with many prior art control systems for powershift transmissions. One such problem was that of providing some means by which the transmission of an off-road vehicle could be controlled to enable the vehicle to be driven in a limited or auxiliary manner even though the controller of the system has malfunctioned. The "limp-home" mode of operation disclosed in the '913 patent provided the ability to at least move the vehicle under its own power to a trailer or a repair facility whereby the vehicle could be repaired or transported to a repair facility.
While the limp-home mode of operation provided by the control system of the '913 patent has proven to be a significant advantage in enabling heavy-duty off-road vehicles to be driven even in the presence of a malfunction of the controller of the system, this system did not provide for any type of electronically modulated control of the transmission while in the limp-home mode. Accordingly, the problems associated with completely manual operation of such transmissions are present while in the limp-home mode of the system of the '913 patent.
Yet another feature provided by the '913 patent was a watchdog timer which monitored operation of the control system, and particularly the microprocessor thereof, and helped to detect a malfunction of the microprocessor. While this feature has also proven to be valuable in increasing the operational integrity of the control system, the watchdog timer of the '913 patent was still powered by the same regulated supply voltage as the microprocessor of the system, and thereby not immune from operational problems when the regulated supply voltage powering the microprocessor operated spuriously. Thus, it was not certain that action taken by the watchdog timer was in fact due to spurious operation of the microprocessor or in fact spurious operation of the watchdog timer itself. In addition, the control system of the '913 patent incorporated no means for monitoring and overriding operation of the watchdog timer in the event of a low voltage condition present in its power regulating circuitry.
With the increasing complexity of powershift transmission systems and the number of variables which are desired to be monitored, there is a need to monitor and control even larger numbers of external sensing and actuating devices. This, in turn, has given rise to a need for an electronic control system for a powershift transmission which is capable of enabling several independent, computer-based control systems to be modularly intercoupled to thereby control and monitor an even greater number of sensor and actuator-type devices used with such transmissions. By including some means by which the microcomputers of independent control systems can communicate, information could be exchanged between the microcomputers of the various control systems to enable significantly increased flexibility and control capability of powershift transmission systems.
With further regard to the above, the ability to enable a microcomputer of an electronic control system for a powershift transmission to communicate with an external device would also enable the microcomputer to be reprogrammed without removing the electronic control system or any components thereof from the vehicle. This would further significantly increase the flexibility and utility of such a control system by enabling operating parameters stored within a memory of the microcomputer and/or the operational code stored in an electrically erasable momory device to be reprogrammed, for example, by a portable computer, at the site of the vehicle without even having to drive the vehicle from the areas at which it is currently operating. Thus, reprogramming could be accomplished in the field quickly, easily and with a minimum of inconvenience and disruption of the operation of the vehicle.
The ability to quickly and easily reprogram the microcomputer of such an electronic control system would further enhance the ability of the control system to more finely and accurately compensate for changing environmental conditions (i.e., unusually steep grades or uneven topography) which the vehicle may be required to negotiate during operation.
Accordingly, it is a principal object of the present invention to provide an electronic control system for a powershift transmission of a heavy-duty off-road vehicle, where the control system incorporates a limp-home mode capable of providing a modulated control signal to control a master clutch of the transmission of the vehicle.
It is another object of the present invention to provide an electronic control system for a powershift transmission of an off-road heavy-duty vehicle, where the control system incorporates a watchdog timer circuit powered independently of a regulated supply voltage used to power a microcomputer of the system to thereby further insure against spurious operation of the watchdog circuit in the event of a low-voltage condition of a regulated supply voltage powering the microcomputer of the system, to thereby increase the integrity of operation of the watchdog timer circuit.
It is still a further object of the present invention to provide an electronic control system having a back-up regulated voltage supply circuit which provides a pulse-width modulated control signal, where the control signal provides pulse-width modulated control over a master clutch of a powershift transmission of a heavy-duty off-road vehicle in the event of a malfunction of a microcomputer of the system or a low-voltage condition of a regulated microcomputer supply voltage.
It is yet another object of the present invention to provide an electronic control system for controlling a powershift transmission of a heavy-duty off-road vehicle, where the system includes means for monitoring a watchdog timer circuit thereof and overriding operation of the watchdog timer circuit upon detection of a malfunction in a regulated supply voltage circuit being used to power the watchdog timer circuit.
It is still a further object of the present invention to provide an electronic control system for a powershift transmission, where the control system is modular and can be coupled in bi-directional communication with a plurality of additional microcomputers of independent, external control systems, to thereby further increase the control capabilities of the system.
It is yet another object of the present invention to provide an electronic control system for a powershift transmission of a heavy-duty, off-road vehicle, where the system incorporates a microcomputer and/or an electrically erasable memory device which may be reprogrammed without removing it from the control system by an external programming device, to thereby enable the microcomputer to be reprogrammed while the vehicle remains at a work site.